High efficiency balanced detection interferometer

Abstract

An interferometer configured for use in optical coherence domain (OCT) reflectometry systems is disclosed. In the preferred embodiments, efficient routing of light and a balanced detection arrangement provide a high signal to noise ratio. In a first set of embodiments, a 3×3 coupler is used to split light along separate sample and reference paths and also for combining light returning from those paths and supplying the interfered collected light to the detection system. In an alternate set of embodiments, a pair of cascaded 2×2 couplers provides a similar function. The interferometer can be used with various OCT modalities including time-domain and frequency domain approaches.

Description

PRIORITY CLAIM PROVISIONAL[0001]This patent application claims priority to U.S. Provisional Patent Application No. 60 / 629,429, filed Nov. 19, 2004, which is incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The invention relates generally to optical imaging using optical coherence tomography and in particular to systems and methods for achieving balanced detection with high signal to noise ratio.[0004]2. Description of Related Art[0005]Optical coherence domain reflectometry (OCDR) is a technique initially developed to provide a higher resolution over optical time domain reflectometry (OTDR) for the characterization of the position and the magnitude of reflection sites in such optical assemblies as optical fiber based systems, miniature optical components and integrated optics (Youngquist et al., “Optical Coherence-Domain Reflectometry: A New Optical Evaluation Technique”, 1987, Optics Letters 12(3):158-160). With the addition of transve...

AI Technical Summary

Benefits of technology

This configuration enhances the signal-to-noise ratio (SNR) by up to 15.5 dB compared to standard Michelson configurations, while reducing system complexity and cost, and allows for compact and efficient optical coherence tomography systems.

Problems solved by technology

However, this configuration is limited to an optical efficiency of 25% as explained below.

Otherwise, the signal will be degraded by the optical power noise of the source.

Hence virtually 75% of the optical power supplied by the light source is wasted in this configuration.

Another issue with the classic Michelson interferometer (FIG. 1) is that light from the reference arm is coupled back into the optical source, causing side effects that can impact the quality of the resulting image.

However, due to the fact that a practical fast-scanning optical delay line operates in reflection mode, a second circulator is needed, and this will increase the cost of the system.

However, in the case of Ai and Aii, although the SNR is maximized, if a retroreflective ODL is desired in these configurations, a second circulator would be necessary which will increase the cost of the system.

The system hence costs more and is not very compact.

For the cases of Ci and Cii, although the system is compact as there is only one 2×2 coupler, the optical power efficiency is not fully maximized as the power splitting ratio of the coupler must be made 50 / 50 for returned dual balanced detection, which will also force the forward split ratio to be 50 / 50.

As a result, attenuation in the reference arm is needed to achieve shot noise limited detection and this will waste optical power.

But these schemes generally require a complicated polarization dependent splitter design and are not very suitable for biological samples with varying birefringence [EP1253398, U.S. patent Application No.

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